1. Field of the Invention
The present invention relates to a wiper device for a vehicle which wipes a windshield glass of an automobile and the like.
2. Description of the Related Art
A wiper device for a vehicle which wipes a windshield glass of an automobile and the like is composed of a wiper arm and a wiper blade held thereby.
In a wiper arm, one end portion of an arm head is fixed to a pivot shaft and a retainer is connected to the other end portion thereof via a spindle so as to be pivotable by a predetermined angle. Between the arm head and the retainer, a spring is hung for urging the retainer constantly toward a surface to be wiped of a windshield glass and the like. An arm piece is fixed to the end portion of the retainer. The end portion of the arm piece is bent substantially in a U-shaped configuration so as to serve as a holding portion, which is connected to and holds a wiper blade. On the other hand, the wiper blade is composed of a blade rubber for wiping by contacting with the surface to be wiped and a plurality of holding levers for holding the blade rubber.
During an operation of the wiper device for a vehicle, the wiper arm and the wiper blade reciprocate pivotally so that the blade rubber moves while in close contact with the windshield glass surface so as to wipe raindrops.
In a wiper device for a vehicle of this kind, a wide-range wiping type equipped with an expanding and contracting wiper arm has been proposed so that as little area as possible is left unwiped (so that the wiping range is expanded) in the whole region of the windshield glass surface. Further, among wiper devices of the wide-range wiping type, a wiper device equipped with a wiper arm referred to as a quadric linking wiper arm is especially known (one example is EP No. 0,182,123).
A wiper device for a vehicle equipped with a wiper arm using the quadric linking mechanism of this kind is provided with a pair of levers consisting of a main lever and a sub-lever. The main lever is connected to and fixed to a pivot shaft, and the sub-lever is pivotally supported by a spindle provided in a position at a predetermined distance from the pivot shaft. Further, not only are the main lever and the sub-lever disposed in parallel with each other, but an arm head is pivotally connected to their respective end portions via their connecting shafts.
When the main lever pivots with the pivot shaft, the arm head is pivoted by the sub-lever which regulates the movement of the arm head in accordance with the pivotal movement of the main lever, while the arm head is moving close to and away from the pivot shaft, with the result that the overall length of the wiper arm is expanded and contracted. Thus, the overall length of the wiper arm is seemingly expanded in a predetermined wiping position, thereby enlarging the wiping range thereof. Therefore, for example, when wiping a windshield glass surface whose lengthwise dimension is set relatively long, unwiped regions are less likely to occur in a whole region of the windshield glass surface compared with a wiper device equipped with a conventional wiper arm (the one wherein an arm head is fixed directly to a pivot shaft around which a wiper arm and a wiper blade simply reciprocates pivotally).
In a wiper device for a vehicle equipped with a wiper arm using the quadric linking mechanism of this kind, the overall length of the wiper arm is seemingly expanded in a predetermined wiping position as described above, thereby enlarging the wiping range thereof. On the other hand, as the wiping operation is conducted by a compound movement consisting of a rotation movement and an expansion and contraction movement, the velocity of rotation (the angular velocity) of the wiper arm (the wiper blade) fluctuates irregularly (becomes quicker or slower) between the upper reversed position and the lower reversed position, thereby leading the driver in some cases to feel uncomfortable.
This is caused by the excessively high fluctuation ratio (fluctuation range) of the angular velocity of rotation of the wiper arm (the wiper blade) between the upper reversed position and the lower reversed position. For example, when the fluctuation of said angular velocity of rotation exceeds the range of 25% of the angular velocity of rotation of a wiper device equipped with a conventional wiper arm (the one wherein an arm head is fixed directly to a pivot shaft around which a wiper arm and a wiper blade simply reciprocates pivotally), most drivers feel uncomfortable.
In addition, when the wiper device includes a second wiper device equipped with a second pivoting shaft which is independent of said pivoting shaft but pivots synchronously with said pivoting shaft, a second arm head which is connected to said second pivoting shaft, and a second wiper arm which is connected to said second arm head and to whose end portion a wiper blade is connected, a driver may feel uncomfortable because the fluctuation in the wiping speed of the wiper device which is equipped with a wiper arm using the quadric linking mechanism of this kind, in relation to that of said second wiper device, is large.